Question

For isothermal reversible expansion of an ideal gas:

• A. $△H>0$ and $△U=0$
• B. $△H>0$ and $△U<0$
• C. $△H=0$ and $△U=0$
• D. $△H=0$ and $△U>0$

Answer 1

The correct option is C $△H=0$ and $△U=0$

For isothermal reversible expansion of ideal gas $\Delta H=0$ and $\Delta U=0$.

For 1 mole of ideal gas,

$\Delta U=C_v\Delta T=0$. [Since $\Delta T=0$ becuase the process is isothermal].

Again,

$\Delta H=\Delta U+\Delta \left(PV\right)=\Delta U+\Delta \left(RT\right)=\Delta U+R\Delta T$

$\Delta H=0+R\Delta T=0+0=0$; [$R\Delta T=0$ since $\Delta T=0$]